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COMPUTED RADIOGRAPHY & ELECTRONIC IMAGING
What Is Digital Imaging?
Digital imaging is the acquisition of images to a computer rather than directly to film.
TERMINOLOGY
 CR Computed Radiography
 DR Digital Radiography
 DDR -Direct to Digital Radiography
CONVENTIAL vs DIGITAL IMAGING
 Currently, most x-ray imaging systems produce an analog image
(radiographs, & fluoroscopy). Using x-ray tube – films in cassettes
 Digital radiography systems require that the electronic signal be converted
to a digital signal - Using x-ray tube – cassettes with phosphor plate
Directed digital radiography, a term used to describe total
Electronic imaging capturing.
Eliminates the need for an image plate altogether.
Methods of Digitizing an Image
 1. Film Digitizer - Teleradiography system (PACS, DICOM)
 2. Video Camera (vidicon or plumbicon)
 3. Computed Radiography (CR)
 4. Direct Radiography (DDR)
Analog to Digital Terminology
 Analog to Digital Converter (ADC) - is an electronic device that changes
the original continuous density (analog signal) into a set of discrete gray
levels (digital signal)
Conventional Image processing time can not change image after processed
 Digital provides a wide (dynamic) range of grays. Windowing in post-processing
can enhance image for proper optical density (OD).
 Teleradiography can send images to other area instantly - “Off site consultation
CR Projectional Radiography
 The Image capture cassette similar to a conventional cassette w/o film.
 CR allows the use of conventional
x-ray equipment.
 CR bridges the gap to fully digital imaging department.
Computed Radiography CR
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“CR”, A term used to describe projection radiography using photostimuable
phosphor (PSP) or storage phosphors.
 X-rays incident on PSP sensor or imaging plate (IP) produces a latent
image that is stored in the IP and stimulated to luminese by laser light.
Eliminates the need for film as a recording medium
Theory of Operations Continued
 “Image in Space” (Latent Image)
 A latent image is retrieved using a laser.
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The phosphor screen is “read” by the storage phosphor - red laser light reader to produce a digital image
Stored energy is released as visible (blue) light.
Light is converted (PMT) into an electrical signal.
The processed image is sent via the network to defined destinations, ie
workstations, and laser printers.
CR CASSETES
Similar looking to “regular” cassettes
 No ID blocker window (blocker used for image orientation
 Less variety of sizes
 Add on “Grids” as required
 Very sensitive
FILM VS MONITORS
FILM
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Cost of supplies
MONITORS
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Cost of service
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Higher resolution increases
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Space requirements
efficiency & saves time
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Processing/
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Reduces space needed for
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Chemicals fumes and
processing and storing
environmental impact
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Images sent to many stations
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IMAGE DISPLAY
FILM vs MONITORS
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In Film- Screen imaging:
 The film serves as both the image receptor and display device.
 The Intensifying Screens serve as the image detector for the latent
image.
In Computed Radiography, the Image plate receives the latent image and
forwards it to the Video Monitor for display.
Obtaining The Image
 The same rules, laws, principles and theories apply when obtaining a
radiographic image.
PACS
 Picture Archival and Communications System
 A system that stores and transfers images, reports and vital patient data
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TERMINOLOGY TELERADIOGRAPHY - Remote Transmission of images
CONTRAST & DENSITY
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Most digital systems are capable of 1024 shades of gray - but the human
eye can see only about 30 shades of gray.
The Optical Density and Contrast can be adjusted after the exposure by
the Radiographer. This is postprocessing.
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General Overview
 PSP cassette exposed by conventional X-ray equipment.
 Latent image generated as a matrix of trapped electrons in the plate.
 Raster scanning of the plate with a laser induces release of trapped e- and
subsequent emission of blue PSL light proportional to incident X-ray
intensity.
 PMT converts PSL into time varying electrical signals that is digitized.
 Plate is erased with high intensity white light and re-used.
 This released light can be captured and converted to a digital signal.
The digital image can be manipulated and transmitted to display and archive
devices.
Histogram Analysis
A histogram is a plot of gray scale value vs. the frequency of occurrence
(# pixels) of the gray value in the image.
CR
 Can use standard X-ray Equip
 Uses photostimulable plate with barium fluoro halide crystal
 can hold image for up to 6 hrs
 H&D curve - more info available in the high & low ranges (Merrills)
Image Reader converts analog image (latent image) on imaging plate to digital then scanned by laser
Image displayed on monitor (replaces viewboxes)
Image enhanced: zoom /contrast/ rotate/
CR - Imaging plate
 Looks like a regular x-ray cassette
 less dose needed ? (tendency to use more due to quantum mottle
 phospor plate inside cassette is removable (thin -flexable- 1mm)
 images can be tailored
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Storage /Archiving
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CONV RAD
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films: bulky
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deteriorates over time
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requires large storage & expense
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environmental concerns
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CR & DR
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8000 images stored on CD-R
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Jukebox storage
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no deterioration of images
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easy access
Advantages of DIGITAL
 Store and retrieve without loss of
quality
 Processing to optimize and improve
image
 Rapid storage and retrieval
 Rapid long distance transmission
 Improved image management
 Economics (?)